You can earn coins by finding bonus words, finishing a set of Wordscapes puzzles, or sometimes as a Daily Gift. You can also earn coins by solving the challenge word in a puzzle. This word will have coins on top of the blank letter squares. Once you solve this word, you will receive those coins and be able to move on to the next level.
Coins are used to purchase hints. You can simply touch the hint buttons to use the coins. For more information on hints, see the Hints and Boosters section of the FAQ.